Thin film transistor substrate and method for forming metal wire thereof

ABSTRACT

The present invention relates to a thin film transistor substrate and a metal wiring method thereof, more particularly to a thin film transistor substrate comprising self-assembled monolayers between the substrate and the metal wiring, and a metal wiring method thereof. Since a thin film transistor substrate of the present invention comprises three-dimensionally cross-linked self-assembled monolayers between the Si surface and the metal wiring, it has good adhesion ability and anti-diffusion ability.

BACKGROUND OF THE INVENTION

(a) Field of the Invention

The present invention relates to a thin film transistor substrate and ametal wiring method thereof, and more particularly to a thin filmtransistor substrate having superior adhesion ability and diffusionresistance and a metal wiring method thereof.

(b) Description of the Related Art

A thin film transistor (TFT) is one of the devices widely used asswitching devices of TFT liquid crystal displays.

A thin film transistor substrate comprises a scanning signal wiring orgate wiring that transfers scanning signals, a picture signal wiring ordata wiring that transfers picture signals, a thin film transistor thatconnects the gate wiring and the data wiring, a pixel electrodeconnected to the thin film transistor, a gate insulation film thatcovers the gate wiring, and a passivation film that protects the thinfilm transistor and the data wiring. A thin film transistor comprises asemiconductor layer that forms a gate electrode and channels, a sourceelectrode, a drain electrode, a gate insulation film and a passivationlayer. A thin film transistor is a switching device that transfers orinterrupts picture signals transferred through the data wiring dependingon scanning signals transferred by the gate wiring.

In TFT LCDs using the thin film transistor as a switching device, anelectric field is applied to the liquid crystal using optical anisotropyand polarization of the liquid crystal. The electric field controlsarrangement orientation of the liquid crystal molecules to offer images.

In the active matrix liquid crystal display (AMLCD), which is beingactively researched and developed, the pixel electrodes connected withthe thin film transistor are arranged in matrix form, so that it canoffer large screen size and high resolution, such as SXGA or UXGA.

In order to make such large-area and high-resolution liquid crystaldisplays as SXGA or UXGA, resistance of gate wiring, data wiring andother wirings should be low. In particular, if the resistance of thegate wiring is high, the image quality worsens because of cross-talksdue to signal delay caused by the wiring resistance. Metals that can beused for the wiring and their characteristics are summarized in thefollowing Table 1. TABLE 1 Specific resistance Adhesion Heat Metal (μΩ ·cm) Price ability resistance Cu 2 Low Low High Au 3 High Low High Al 4Low High Low Mo 20 Moderate High High Cr 50 Moderate High High

As seen in Table 1, aluminum has low heat resistance. While copper issatisfactory in cost and heat resistance, it has poor adhesion abilityto the substrate. Therefore, many researches are trying to improve theadhesion ability of copper to the substrate.

In this regard, wirings of copper alloys, such as Cu/Ti/Si, Cu/TiN/Si,Cu/Ta/Si and Cu/TaN/Si, are widely used. However, these copper alloywirings are manufactured through complicated processes. Also, they haveweak adhesion of Si and Cu, and the anti-diffusion films are thick.Moreover, the anti-diffusion films react with Cu during heat treatment.

Recently, the copper-silver alloy wirings are widely used. However,silver has weak adhesion ability to the glass substrate or siliconlayers. The weak adhesion ability causes problems like the thin film'scoming off from the substrate or breaking of the wiring. Also, silver iseasily damaged by dry-type etching agents for etching insulation filmconsisting of silicon nitride, etc.

SUMMARY OF THE INVENTION

The present invention relates to a thin film transistor substrate and ametal wiring method thereof, more particularly to a thin film transistorsubstrate comprising self-assembled monolayers between the substrate andmetal wiring and a metal wiring method thereof.

The thin film transistor substrate of the present invention hascross-linked self-assembled monolayers between Si surface and metalwiring, thereby offering good adhesion ability and anti-diffusionability.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 a and 1 b show copper or copper alloy wiring structure, whereinan anti-diffusion film is formed between the Si surface and Cu.

FIGS. 2 a to 2 d show AES (Auger electron spectrometer) depth profilesof copper (Cu) wiring, wherein self-assembled monolayers are formedbetween the Si surface and Cu or Cu(Ag), before and after heat treatmentat 300° C.

FIG. 3 is a graph that shows change in specific resistance of copper orcopper alloy on top of the self-assembled monolayers according to thetemperature.

FIGS. 4 a and 4 b show a thin film transistor substrate for a liquidcrystal display of the present invention.

FIGS. 5 a and 5 b are cross-sectional views along the line V-V′ of FIGS.4 a and 4 b, respectively.

FIGS. 6 a, 7 a, 8 a and 9 a show a thin film transistor substrate for aliquid crystal display of the present invention, which is being preparedby a sequential process.

FIG. 6 b is a cross-sectional view along the line VIb-VIb′ of FIG. 6 a.

FIG. 7 b is a cross-sectional view along the line VIIb-VIIb′ of FIG. 7 aand shows the step next to that of FIG. 6 b.

FIG. 8 b is a cross-sectional view along the line VIIIb-VIIIb′ of FIG. 8a and shows the step next to that of Fig. FIG. 7 b.

FIG. 9 b is a cross-sectional view along the line IXb-IXb′ of FIG. 9 aand shows the step next to that of FIG. 8 b.

FIG. 10 is a diagrammatic view of a thin film transistor substrate for aliquid crystal display of the present invention.

FIG. 11 is a cross-sectional view along the line XI-XI′ of FIG. 10.

FIG. 12 is a cross-sectional view along the line XII-XII′ of FIG. 10.

FIG. 13 a is a diagrammatic view of a thin film transistor substrate fora liquid crystal display of the present invention.

FIGS. 13 b and 13 c are cross-sectional views along the linesXIIIb-XIIIb′ and XIIIc-XIIIc′ of FIG. 13 a, respectively.

FIGS. 14 a and 14 b are cross-sectional views along the linesXIIIb-XIIIb′ and XIIIc-XIIIVc′ of FIG. 13 a, respectively, which showthe step next to that of FIG. 13 b and FIG. 13 c.

FIG. 15 a is a diagrammatic view of a thin film transistor substrate atthe step next to that of FIGS. 14 a and 14 b.

FIGS. 15 b and 15 c are cross-sectional views along the lines XVb-XVb′and XVc-XVc′ of FIG. 15 a.

FIGS. 16 a, 17 a and 18 a and FIGS. 16 b, 17 b and 18 b arecross-sectional views along the lines XVb-XVb′ and XVc-XVc′ of FIG. 15a, respectively, and show the steps following that of FIGS. 15 b and 15c.

FIG. 19 a and FIG. 19 b are cross-sectional views of a thin filmtransistor substrate at the step next to that of FIGS. 18 a and 18 b.

FIG. 20 a is a diagrammatic view of a thin film transistor substrate atthe step next to that of FIG. 19 a and FIG. 19 b.

FIGS. 20 b and 20 c are cross-sectional views along the lines XXb-XXb′and XXc-XXc′ of FIG. 20 a, respectively.

DETAILED DESCRITPION OF THE PREFERRED EMBODIMENTS

An object of the present invention is to provide a thin film transistorsubstrate having superior adhesion ability to the substrate and superioranti-diffusion ability.

It is another object of the present invention to provide a liquidcrystal display comprising the thin film transistor substrate.

It is still another object of the present invention to provide a metalwiring method of the thin film transistor substrate.

In order to achieve these objects, the present invention provides a thinfilm transistor substrate characterized by comprising self-assembledmonolayers between the substrate and metal wiring.

The present invention also provides a liquid crystal display comprisingthe thin film transistor substrate.

The present invention also provides a metal wiring method of a thin filmtransistor substrate, which comprises: (a) a step of formingself-assembled monolayers by coating self-assembled monolayers (SAMs)forming coating composition on the substrate and heat-treating it; (b) astep of depositing metal wiring material on the substrate; and (c) astep of heat-treating the substrate.

Hereunder is given a more detailed description of the present inventionA thin film transistor substrate of the present invention ischaracterized by self-assembled monolayers formed between the substrateand metal wiring.

For self-assembled monolayers forming materials,3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane,2-aminoundecyltrimethoxysilane, aminophenyltrimethoxysilane,

N-(2-aminoethylaminopropyl)trimethoxysilane, methyltrimethoxysilane,propyltriacetoxysilane and (3-mercaptopropyl)trimethoxysilane arepreferable.

Since self-assembled monolayers formed from these silane compounds havethree-dimensional cross-linkages, they offer good adhesion ability tothe substrate. Also they prevent diffusion of copper to the substratesurface. Therefore, they are useful in preparing high-qualitysubstrates.

In order to prepare a thin film transistor substrate, the self-assembledmonolayers are preferred to have 2 to 3 nm of thickness.

A metal wiring is formed on the self-assembled monolayers. For the metalwiring material, copper or copper alloy is preferred. For the metal usedin the copper alloy, Ag, Mg, B, Ca, Al, Li, Np, Pu, Ce, Eu, Pr, La, Nd,Sm, Zn or any mixture thereof are preferred.

When a copper alloy is used for the metal wiring material the metalcomponent, i.e., Ag, Mg, B, Ca, Al, Li, Np, Pu, Ce, Eu, Pr, La, Nd, Sm,Zn or any mixture thereof, diffused to the substrate or film surfaceserves as an anti-diffusion film together with the self-assembledmonolayers. Since these metals have lower surface energy than copper,they have desirable contact resistance. Particularly, Ag offers superioranti-diffusion ability because it is not fairly soluble to Si.

In a thin film transistor substrate comprising self-assembled monolayersbetween the substrate and metal wiring according to the presentinvention, the substrate is preferably a glass substrate, ann+a-Si/a-Si/SiN three-layer substrate, or an Si, SiO₂ or other low-k(k<3.5) substrate.

When self-assembled monolayers are formed in a glass substrate, ann+a-Si/a-Si/SiN three-layer substrate, or an Si, SiO₂ or other low-k(k<3.5) substrate, which is used for a thin film transistor substrate ofthe present invention, a silicide is formed to offer superior adhesionto the lower substrate and prevents diffusion of copper to thesubstrate.

A metal wiring method of a thin film transistor substrate of the presentinvention is as follows.

Firstly, self-assembled monolayers (SAMs) forming coating composition iscoated on the substrate and heat-treated to form self-assembledmonolayers (SAMs) [Step (a)].

For the self-assembled monolayers forming material,3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane,2-aminoundecyltrimethoxysilane, aminophenyltrimethoxysilane,N-(2-aminoethylaminopropyl)trimethoxysilane, methyltrimethoxysilane,propyltriacetoxysilane and (3-mercaptopropyl)trimethoxysilane arepreferable.

To form self-assembled monolayers on the substrate, the self-assembledmonolayers forming material should be dissolved in a solvent, coated onthe substrate and hardened by heat treatment. For the solvent, alcoholslike methanol, ethanol, propanol and butanol, cellusolv solvents likemethyl cellusolv, dimethylformamide or water are preferred.

Mixing ration of the silane compound, a self-assembled monolayersforming material, and the solvent is preferably 1:20 to 1:30 by weight.

The self-assembled monolayers forming material can be coated on thesubstrate by dipping, spinning, spraying or printing.

After the substrate self-assembled monolayers forming material dissolvedin the solvent is coated on the substrate, it is heat-treated andhardened to form self-assembled monolayers. The heat treatmenttemperature is preferably 100 to 300° C., so that the silane compoundcan be condensed.

In a thin film transistor substrate having self-assembled monolayersaccording to the present invention, a glass substrate, ann+a-Si/a-Si/SiN three-layer substrate, or an Si, SiO₂ or other low-k(k<3.5) substrate can be preferably used for the substrate.

After self-assembled monolayers are formed on the substrate, a metalwiring material is deposited on it [Step (b)]. For the metal wiringmaterial, copper or copper alloy is preferable. For the alloy component,a metal having lower surface energy than copper, such as Ag, Mg, B, Ca,Al, Li, Np, Pu, Ce, Eu, Pr, La, Nd, Sm, Zn or any mixture thereof, ispreferable. In the copper alloy, the alloy component is preferably addedin 0.1 to 15 wt % to copper.

Then, the substrate with the metal wiring material deposited isheat-treated [Step {circle around (c)}]. The heat treatment ispreferably carried out at 100 to 300° C. in vacuum.

If Ti, TiN, Ta or TaN, which is used as conventional anti-diffusionfilm, is heat-treated, copper reacts with the anti-diffusion film toincrease specific resistance. However, the self-assembled monolayers ofthe present invention do not react with copper when heat-treated.Therefore, the specific resistance does not increase and a thinanti-diffusion film of nanometer dimension is obtained.

FIGS. 1 a and 1 b show a copper or copper alloy wiring structure,wherein self-assembled monolayers are formed between Si surface and Cu.In FIG. 1 a, only copper was used; and in FIG. 1 b, copper-silver alloywas used. As seen in FIG. 1 b, the copper-silver alloy offers an Aglayer on the self-assembled monolayers to form a three-layer structure.Therefore, diffusion of copper to the Si surface can be prevented moreeffectively.

FIGS. 2 a and 2 b are AES depth profiles of a copper (Cu) wiring,wherein self-assembled monolayers are formed between the Si surface andCu, before and after heat treatment at 300° C. FIGS. 2 c and 2 d are AESdepth profiles of a copper alloy [Cu(Ag)] wiring, wherein self-assembledmonolayers are formed between the Si surface and Cu, before and afterheat treatment at 300° C. AES (Auger electron spectrometer) analysis isa method of detecting substances in a specimen by sputtering electronsto the specimen.

As seen in FIG. 2 a to FIG. 2 d, Cu was hardly detected after 15 secondsof sputtering. It shows that the self-assembled monolayers formedbetween the Si surface and copper or copper alloy effectively preventsdiffusion of Cu to the Si surface. Therefore, they can be utilized tomake a thin film transistor substrate having a superior anti-diffusionability. In particular, a superior anti-diffusion ability can bemaintained even at about 400° C. if a copper alloy is used as wiringmaterial.

FIG. 3 is a graph that shows change in specific resistance of copper orcopper alloy on top of the self-assembled monolayers according to thetemperature. In a thin film transistor substrate of the presentinvention, the self-assembled monolayers formed at the bottom of thecopper or copper alloy wiring inhibits reaction of copper with theanti-diffusion film during heat treatment. Therefore, the specificresistance does not increase.

Hereunder is given a specific description of a thin film transistorsubstrate according to the present invention.

A thin film transistor substrate of the present invention comprises: aninsulation substrate; a first signal line formed on the insulationsubstrate; a first insulation film formed on the first signal line; asecond signal line formed on the first insulation film and crossing withthe first signal line; a thin film transistor electrically connectedwith the first signal line and the second signal line; a secondinsulation film formed on the thin film transistor and having a firstcontact opening that exposes electrodes of the thin film transistor; andpixel electrodes formed on the second insulation film and connected withelectrodes of the thin film transistor through the first contactopening. At least one of the first signal line or the second signal linehas a copper or copper alloy wiring comprising a two-layer structure ofself-assembled monolayers and a Cu layer.

Referring to the attached drawings, a wiring method of thin filmtransistor substrate of the present invention is explained below, takinga thin film transistor liquid crystal display as an example.

FIG. 4 a shows a thin film transistor substrate for a liquid crystaldisplay of the present invention, and FIG. 5 a is a cross-sectional viewof the thin film transistor substrate along the line V-V′ of FIG. 4 a.

A gate wiring 22, 24, 26 having a two-layer structure of first gatewiring layer 221, 241, 261 and a second gate wiring layer 222, 242, 262is formed on an insulation substrate 10. The first gate wiring layer221, 241, 261 is made of self-assembled monolayers and the second gatewiring layer 222, 242, 262 is made of copper or copper alloy. The firstgate wiring layer 221, 241, 261 is formed to improve adhesion to thesubstrate 10. Preferably, the first gate wiring layer 221, 241, 261 hasa thickness ranging from 2 to 3 nm. The second gate wiring layer 222,242, 262 functions as a path for electric signal and is made of copperor copper alloy with low specific resistance.

The gate wiring 22, 24, 26 comprises a gate line 22 stretchinghorizontally and a gate electrode 26 connected with the gate line 22.One end 24 of the gate line 22 has an extended width for connection withan external circuit.

On the substrate 10, a gate insulation film 30 made of a silicon nitride(SiN_(x)), etc. covers the gate wiring 22, 24, 26.

On top of the gate insulation film 30 of the gate electrode 24, asemiconductor layer 40 made of semiconductor like amorphous silicon isformed. And, on the semiconductor layer 40, a ohmic contact layer 55, 56made of substances like n+ hydrogenated amorphous silicon, whereinsilicides or n-type impurities are doped in high concentration, isformed.

On the ohmic contact layer 55, 56 and the gate insulation film 30, adata wiring 62, 65, 66, 68 consisting of two layer of a first datawiring layer 621, 651, 661, 681 and a second data wiring layer 622, 652,662, 682, is formed. The first data wiring layer 621, 651, 661, 681 ismade of self-assembled monolayers, and the second data wiring layer 622,652, 662, 682 is made of copper or copper alloy. The first data wiringlayer 621, 651, 661, 681 is formed to enhance adhesion of the ohmiccontact layer 55, 56 to the gate insulation film 30. Preferably, thefirst data wiring layer 621, 651, 661, 681 has a thickness ranging from2 to 3 nm. The second data wiring layer 622, 652, 662, 682 functions asa path for electric signal and is made of copper or copper alloy thathas low specific resistance.

The data wiring 62, 65, 66, 68 comprises a data line 62 formedvertically and defines a pixel by crossing with the gate line 22, asource electrode 65 branching from the data line 62 and extended to theupper part of the ohmic contact layer 54, and a drain electrode 66separated from the source electrode 65 and formed on top of the ohmiccontact layer 56 on the opposite side of the source electrode 65 withthe gate electrode 26 at the center. One end 68 of the data line 62 hasa widened width for connection with an external circuit.

On the data wiring 62, 65, 66, 68 and the semiconductor layer 40 notcovered by it, a protection film 70 consisting of a silicon nitride(SiNx) film, an a-Si:C:O film or an a-Si:O:F film (low-k CVD film)deposited by the PECVD (plasma enhanced chemical vapor deposition)method, and acrylic insulation film, etc., is formed. The a-Si:C:O filmand the a-Si:O:F film (low-k CVD film) deposited by the PECVD methodhave very low dielectric constant (k ranging from 2 to 4). Accordingly,there arises no problem of parasitic capacitance even with a thinthickness. And, adhesion to other films and step coverage are superior.Also, the inorganic CVD film offers superior heat resistance to organicinsulation films. Moreover, the A-Si:C:O film and the a-Si:O:F film(low-k CVD film) deposited by the PECVD method offers 4 to 10 timesfaster deposition and etching rate than a silicon nitride film.

On the protection film 70, a contact opening 76 exposing the drainelectrode 66, a contact opening 78 exposing the end part of the dataline 68, and a contact opening 74 exposing the end part of the gate line24 together with the gate insulation film 30 are formed. The contactopenings 74, 78 exposing the end parts of the date line and the gateline 24, 68 may have polygonal or circular shapes. Preferably, areas ofthe contact openings 74, 78 range from 0.5 mm×15 μm to 2 mm×60 μm.

On the protection film 70, a pixel electrode 82 electrically connectedwith the drain electrode 66 through the contact opening 76 and locatedat a pixel area is formed. Also, contact supporting members 86, 88 areformed on the protection film 70 through the contact openings 74, 78.The pixel electrode 82 and the contact supporting members 86, 88 aremade of ITO (indium tin oxide) or IZO (indium zinc oxide).

The pixel electrode 82 makes a maintenance capacitor in parallel withthe gate line 22, as seen in FIG. 4 and FIG. 5 a. In case maintenancecapacitance is insufficient, additional wiring may be added in the layerof the gate wiring 22, 24, 26.

The opening ratio can be maximized by having the pixel electrode 82 andthe data line 62 overlap. Even if the pixel electrode 82 is overlappedwith the data line 62 to maximize the opening ratio, parasiticcapacitance can be minimized if a low-k CVD film, etc. is used.

Now, a preparing method of a thin film transistor substrate of thepresent invention will be explained in detail, referring to FIG. 4, FIG.5 a, and FIGS. 6 a to 10 b.

Firstly, a first gate wiring layer 221, 241, 261 and a second gatewiring layer 222, 242, 262 are applied on a substrate 10 andphoto-etched to form a gate line 22, a gate electrode 26 and a gatewiring 22, 24, 26 including the end part of the gate line 24 andextending horizontally, as in FIGS. 6 a and 6 b.

Next, a gate insulation film 30 consisting of silicon nitride, asemiconductor layer 40 consisting of amorphous silicon and a dopedamorphous silicon layer 50 are applied, and the semiconductor layer 40and the doped amorphous silicon layer 50 are photo-etched to form asemiconductor layer 40 and a ohmic contact layer 50 of an island shapeon the gate insulation film 30 on top of the gate electrode 24, as inFIGS. 7 a and 7 b.

Then, a first data wiring layer 621, 651, 661, 681 and a second datawiring layer 622, 652, 662, 682 are applied and photo-etched to form adata wiring comprising a data line 62 crossing with the gate line 22, asource electrode 65 connected with the data line 62 and extended to theupper part of the gate electrode 26, an end part of the data line 68connected to the data line 62, and a drain electrode 66 separated fromthe source electrode 64 and opposing the source electrode 65 with thegate electrode 26 at the center, as in FIGS. 8 a and 8 b.

Subsequently, an amorphous silicon layer pattern 50 not covered by thedata wiring 62, 65, 66, 68 is etched to separate the gate electrode 26in two parts and to expose a semiconductor layer pattern 40 between thedoped amorphous silicon layers 55, 56 on both sides. Preferably, theexposed semiconductor layer 40 surface is stabilized with an oxygenplasma.

Next, a silicon nitride film, an a-Si:C:O film or an a-Si:O:F film isgrown by the chemical vapor deposition (CVD) method or an organicinsulation film is coated to form a protection film 70, as in FIGS. 9 aand 9 b.

Subsequently, the gate insulation film 30 and the protection film 70 arepatterned by photo-etching to form contact openings 74, 76, 78 thatexpose the end part of the gate line 24, the drain electrode 66 and theend part of the data line 68. The contact openings 74, 76, 78 may havepolygonal or circular shapes. Preferably, areas of the contact openings74, 78 exposing the end parts 24, 68 range from 0.5 mm×15 μm to 2 mm×60ƒm.

Lastly, an ITO or IZO film is deposited and photo-etched to form a pixelelectrode 82 connected to the drain electrode 66 through the firstcontact opening 76, an end part of the supporting gate line 86 connectedto the end part of the gate line 24 through the second contact opening74, and an end part of the supporting data line 88 connected to the endpart of the data line 68 through the third contact opening 78, as inFIGS. 4 and 5. Preferably, nitrogen gas is used in the pre-heatingprocess before depositing ITO or IZO. This is to prevent formation of ametal oxide film on metal films 24, 66, 68 exposed through the contactopenings 74, 76, 78.

As explained above, the gate wiring and the data wiring are made ofsilver or silver alloy and a protection layer is formed to protect thesilver or silver alloy layer and the adhesion layer, in order to offer alow-resistance wiring and improve wiring reliability.

In the present invention, both the gate wiring and the data wiring areformed in two layers. However, only one of the two wirings may be formedin tow layers, if necessary.

FIG. 5 b is a cross-sectional view along the line V-V′ of FIG. 4 b. Itshows a COA (Color filter On Array) structure of a thin film transistorsubstrate prepared using five masks according to the present invention.The present invention can be equally applied to a COA structure of athin film transistor substrate prepared with four masks.

A double-layer gate wiring consisting of self-assembled monolayers 241,221, 261 and a copper layer 242, 222, 262 is formed on an insulationsubstrate 10. The gate wiring comprises a scanning signal line or a gateline 22 stretching horizontally, and a gate electrode 26 connected tothe end of the gate line 22 and accepting scanning signals from outside.A protruding part of the gate line 22 is overlapped with a conductorpattern for maintenance capacitor 64 connected with the pixel electrode82 to make a maintenance capacitor for improving charge retainingability of the pixel.

On the gate wiring 22, 24, 26 and the substrate 10, a gate insulationfilm 30 made of silicon nitride (SiN_(x)), etc. is formed. The gateelectrode 24 is covered with a gate insulation film 30.

On the gate insulation film pattern 30, a semiconductor pattern 40 madeof semiconductors like hydrogenated amorphous silicon is formed. On thesemiconductor pattern 40, an ohmic contact layer 55, 56 made ofamorphous silicon, etc. doped with a high concentration of n-typeimpurities like phosphorus (P) is formed.

On the ohmic contact layer 55, 56, a source electrode 65 and a drainelectrode 66 made of conductors like Mo or MoW alloy, Cr, Al or Alalloy, Ta, etc. are formed. The data wiring is formed vertically andalso comprises a data line 62 formed vertically and connected with thesource electrode 65, a data pad 68 connected to one end of the data line62 and accepting picture signals from outside, and a conductor patternfor maintenance capacitor 64 overlapping with the protruding part of thegate line 22.

Preferably, the data wiring 62, 64, 65, 66, 68 also has a two-layerstructure of self-assembled monolayers 621, 641, 651, 661, 681 andcopper layer 622, 642, 652, 662, 682, like the gate wiring 22, 24, 26,or a three-layer structure of self-assembled monolayers, silver layerand copper layer.

The ohmic contact layer 55, 56 lowers contact resistance of thesemiconductor pattern 40 and the data wiring 62, 64, 65, 66, 68.

Although not depicted on the figures, an inter-layer insulation filmmade of insulators like silicon oxide or silicon nitride may be formedon the data wiring 62, 64, 65, 66, 68 and the semiconductor pattern 40not covered by the data wiring.

In the pixel area on the gate insulation film 30, red, green and bluecolor filters (R, G, B) having openings C1, C2 that expose the drainelectrode 65 and the conductor pattern for maintenance capacitor 64 areformed vertically. Although the boundaries of the red, green and bluecolor filters (R, G, B) are depicted to fit the upper part of the dataline 62, they may block lights leaked out of the pixel area.

On the red, green and blue color filters 81, 82, 83, a protection film70 made of acrylic organic insulation material or SiOC or SiOF havinggood flattening property and dielectric constant lower than 4.0 isformed by the chemical vapor deposition. This protection film 90 hascontact openings 74, 78, 76, 72 that expose the end part of the gateline 24, the end part of the data line, the drain electrode 66 and theconductor pattern for maintenance capacitor 64, together with the gateinsulation film 30. The contact openings 76, 72 that expose the drainelectrode 66 and the conductor pattern for maintenance capacitor 64 arelocated inside of the openings C1, C2 of the color filters (R, G, B). Asexplained above, the same pattern as that of the inter-layer insulationfilm is obtained, if an inter-layer insulation film is added to thelower part of the color filters (R, G, B).

On the protection film 70, a pixel electrode 82 accepting picturesignals from the thin film transistor and generating an electric fieldtogether with the electrode of the upper layer is formed. The pixelelectrode 82 is made of transparent conducting material like ITO (indiumtin oxide) or IZO (indium zinc oxide), and is connected with the drainelectrode 66 physically and electrically to accept picture signals. Thepixel electrode 82 is overlapped with the gate line 22 and the data line62 to enhance the opening ratio. However, they may not be overlapped.The pixel electrode 82 is also connected with the conductor pattern formaintenance capacitor 64 through the contact opening 72 to transferpicture signals to the conductor pattern 64. On the end part of the gateline 24 and the end part of the data line 68, contact supporting members84, 88 connected with the end parts 24,68 through the contact openings74, 78 are formed. The contact supporting members 84, 88 supportadhesion of the end part of the data line 68 and the end part of thegate line 24 to external circuits and protect the pad. Use of thecontact supporting members 84, 88 is not mandatory but optional.

The above method can be equally applied to preparation of a thin filmtransistor substrate for a liquid crystal display using four masks.

Referring to FIGS. 10 to 12, a unit pixel structure of a thin filmtransistor substrate for a liquid crystal display according to thepresent invention prepared with four masks will be explained in detail.

FIG. 10 is a diagrammatic view of a thin film transistor substrate for aliquid crystal display according to a second example of the presentinvention, and FIG. 11 and FIG. 12 are cross-sectional views along thelines XI-XI′ and XII-XII′ of FIG. 10, respectively.

Firstly, a gate wiring 22, 24, 26 comprising a double layer of the firstgate wiring layer 221, 241, 262 and the second gate wiring layer 222,242, 262 is formed on an insulation substrate 10 as in the firstexample. The first gate wiring layer 221, 241, 261 is made ofself-assembled monolayers and the second gate wiring layer 222, 242, 262is made of copper or copper alloy. The first gate wiring layer 221, 241,261 is formed to improve adhesion to the substrate 10. Preferably, thefirst gate wiring layer 221, 241, 261 has a thickness ranging from 2 to3 nm. The second gate wiring layer 222, 242, 262 functions as a path forelectric signal and is made of copper or copper alloy with low specificresistance. The gate wiring comprises a gate line 22, and end part ofthe gate line 24 and a gate electrode 26.

On the substrate 10, a maintenance electrode line 28 is formed parallelto the gate line 22. The maintenance electrode line 28 also has atwo-layer structure of a first gate wiring layer 281 and a second gatewiring layer 282. The maintenance electrode line 28 is overlapped with aconductor pattern for maintenance capacitor 68 connected with a pixelelectrode 82 to make a maintenance capacitor for improving chargeretaining ability of the pixel. If the maintenance capacitance due tothe overlap of the pixel electrode 82 and the gate line 22 isinsufficient, the maintenance electrode line 28 may not be formed. It iscommon that a voltage equal to that applied to the common electrode ofthe upper substrate is applied to the maintenance electrode line 28.

On the gate wiring 22, 24, 26 and the maintenance electrode line 28, agate insulation film 30 made of silicon nitride (SiN_(x)), etc. isformed. The gate insulation film 30 covers the gate wiring 22, 24, 26and the maintenance electrode line 28.

On the gate insulation film 30, a semiconductor pattern 42, 48 made ofsemiconductors like hydrogenated amorphous silicon is formed. On thesemiconductor pattern 42, 48, an ohmic contact layer pattern or anintermediate layer pattern 55, 56, 58 made of amorphous silicon, etc.doped with a high concentration of n-type impurities like phosphorus (P)is formed.

On the ohmic contact layer pattern 55, 56, 58, a data wiring 62, 64, 65,66, 68 having a three-layer structure of a first data wiring layer 621,641, 651, 661, 681 and a second data wiring layer 622, 642, 652, 662,682 is formed. The first data wiring layer 621, 641, 651, 661, 681 ismade of self-assembled monolayers and the second data wiring layer 622,642, 652, 662, 682 is made of copper or copper alloy. The first datawiring layer 621, 641, 651, 661, 681 is formed to improve adhesion ofthe ohmic contact layer 55, 56 to the gate insulation film 30.Preferably, the first data wiring layer 621, 641, 651, 661, 681 has athickness ranging from 2 to 3 nm. The second data wiring layer 622, 642,652, 662, 682 functions as a path for electric signals and is made ofcopper or copper alloy having low specific resistance. The data wiringcomprises a data line 62 formed vertically, an end part of the data line68 connected with one end of the data line 62 and accepting picturesignals from outside, and a data line part 62, 68, 65 consisting of asource electrode 65 branching from the data line 62. It also comprises adrain electrode 66 separated from the data line part 62, 68, 65 andlocated at the opposite side of the source electrode 65 with referenceto a channel part {circle around (c)}, and a conductor pattern formaintenance capacitor 64 located on a maintenance electrode line 28. Incase the maintenance electrode line 28 is not formed, the conductorpattern for maintenance capacitor 64 is not formed, either.

A contact layer pattern 55, 56, 58 lowers contact resistance of thesemiconductor pattern 42, 48 and the data wiring 62, 64, 65, 66, 68. Ithas a structure completely identical to that of the data wiring 62, 64,65, 66, 68. That is, the intermediate layer pattern of the data linepart 55 is identical to the data line part 62, 68, 65; an intermediatelayer pattern for a drain electrode 56 is identical to the drainelectrode 66; and an intermediate layer pattern for a maintenancecapacitor 58 is identical to the conductor pattern for maintenancecapacitor 64.

The semiconductor pattern 42, 48 has a structure identical to that ofthe data wiring 62, 64, 65, 66, 68 and the ohmic contact layer pattern55, 56, 58 except the channel part {circle around (c)} of the thin filmtransistor. To be specific, the semiconductor pattern for maintenancecapacitor 48, the conductor pattern for maintenance capacitor 64 and thecontact layer pattern for maintenance capacitor 58 have the samestructure, but the semiconductor pattern for a thin film transistor 42is a little different from the other part of the data wiring and thecontact layer pattern. That is, while the data line part 62, 68, 65,especially the source electrode 65 is separated from the drain electrode66 and the intermediate layer of the data line part 55 and the contactlayer pattern for a drain electrode 56 are separated from each other atthe channel part {circle around (c)} of the thin film transistor, thesemiconductor pattern for a thin film transistor 42 is connected at thechannel part {circle around (c)} to form a channel for the thin filmtransistor.

On the data wiring 62, 64, 65, 66, 68, a protection film 70 consistingof a silicon nitride film, an a-Si:C:O film or an a-Si:O:F film (low-kCVD film) deposited by the PECVD (plasma enhanced chemical vapordeposition) method or an organic insulation film is formed. Theprotection film 70 has contact openings 76, 78, 72 that expose the drainelectrode 66, the end part of the data line 64 and the conductor patternfor maintenance capacitor 68. It also has a contact opening 74 thatexposes the end part of the gate line 24 together with the gateinsulation film 30.

On the protection film 70, a pixel electrode 82 is made of transparentconducting material like ITO (indium tin oxide) or IZO (indium zincoxide), and is connected with the drain electrode 66 physically andelectrically to accept picture signals. The pixel electrode 82 isoverlapped with the gate line 22 and the data line 62 to enhance theopening ratio. However, they may not be overlapped. The pixel electrode82 is also connected with the conductor pattern for maintenancecapacitor 64 through the contact opening 72 to transfer picture signalsto the conductor pattern 64. On the end part of the gate line 24 and theend part of the data line 68, an end part of a supporting gate line 86and an end part of a supporting data line 88 connected through thecontact openings 74, 78 are formed. These support adhesion of the endparts 24, 68 to external circuits and protect them. Use of the end partof a supporting gate line 86 and the end part of a supporting data line88 is not mandatory but optional.

Now, a method of preparing a thin film transistor substrate for a liquidcrystal display having the structure of FIG. 10 to FIG. 12 with fourmasks will be explained in detail, referring to FIGS. 11 to 13 and FIGS.13 a to 20 c.

Firstly, a first gate wiring layer 221, 241, 261, 281 and a second gatewiring layer 222, 242, 262, 282 are applied as in the first example, andphoto-etched to form a gate wiring comprising a gate line 22, an endpart of the gate line 24 and a gate electrode 26, and a maintenanceelectrode line 28, as in FIGS. 13 a to 13 c.

Next, a gate insulation film 30 consisting of silicon nitride, asemiconductor layer 40 and an intermediate layer 50 are continuouslydeposited by the chemical vapor deposition method to the thicknessesranging from 1,500 Å to 5,000 Å, from 500 Å to 2,000 Å and from 300 Å to600 Å, respectively, as in FIGS. 14 a and 14 b. Then, a first conductionfilm 601 and a second conduction film 602 for forming a data wiring aredeposited by the sputtering method, etc. to form a conductor layer 60.Then, a photosensitive film 110 is applied to 1 μm to 2 μm of thicknesson it.

Then, the photosensitive film 110 is exposed to light through a mask anddeveloped to form a photosensitive film pattern 112, 114, as in FIGS. 15b and 15 c. In the photosensitive film pattern 112, 114, the channelpart {circle around (c)} of the thin film transistor, or the first part114 between the source electrode 65 and the drain electrode 66, isformed to have smaller thickness than the data wiring part (A), or thesecond part 112 wherein the data wiring 62, 64, 65, 66, 68 will beformed. In the remaining part (B), the photosensitive film is completelyremoved. The thickness ratio of the photosensitive film 114 remaining inthe channel part (C) and the photosensitive film 112 remaining in thedata wiring part (A) shall be different according to the etchingcondition. Preferably, the tackiness of the first part 114 is smallerthan ½ of the tackiness of the second part 112. For example, it ispreferred to be smaller than 4,000 Å.

The thickness of the photosensitive film can be varied in many ways.Typically, a slit- or lattice-type pattern is formed or asemi-transparent film is used to control light transmission to the (A)part.

Preferably, the linewidth or gap of the slit pattern is smaller than theresolution of a light exposing means. In case a semi-transparent film isused, thin films with different transmissivity or thin films withdifferent thickness may be used.

If light is exposed to the photosensitive film using such a mask,polymers are completely decomposed at the part where the light contactsdirectly. In the part where a slit pattern or a semi-transparent film isformed, polymers are not completely decomposed. In the part wherecovered by a shading film, polymers are hardly decomposed. If thephotosensitive film is developed, only the part where polymers are notdecomposed remain. Therefore, the part exposed to a small amount oflight has a smaller thickness than the part not exposed to light. Theexposing time should not be too long, lest all polymers should bedecomposed.

Such a thin photosensitive film 114 can also be formed by using aphotosensitive film made of reflowable material and a usual mask havinglight-transmitting and non-transmitting parts, and exposing, developingand reflowing the photosensitive film, so that part of thephotosensitive film flows to the part where no photosensitive filmremains.

Then, the photosensitive film pattern 114 and the films below it, thatis the conductor layer 60, the intermediate layer 50 and thesemiconductor layer 40, are etched. In the data wiring part (A), thedata wiring and the films below it should remain; in the channel part(C), only the semiconductor layer should remain; and in the remainingpart (B), all the three layers 60, 50, 40 should be removed to exposethe gate insulation film 30.

The exposed conductor layer 60 of the remaining part B is removed toexpose the intermediate layer 50 below it, as in FIGS. 16 a and 16 b. Inthis process, either dry etching or wet etching method can be used.Preferably, the etching is performed under a condition where theconductor layer 60 is etched and the photosensitive film pattern 112,114 is hardly etched. However, because it is difficult to find such acondition for dry etching, a condition where the photosensitive filmpattern 112, 114 is also etched is allowed. In this case, the first part114 should be thicker than for wet etching, lest the first part 114should be removed to expose the conductor layer 60 below it.

As a result of this process, only the conductor layer of the channelpart (C) and the and data wiring part (B), that is the conductor patternfor source/drain 67 and the conductor pattern for maintenance capacitor68, remain and the conductor layer 60 of the remaining part (B) iscompletely removed to expose the intermediate layer 50 below it, as inFIGS. 16 a and 16 b. The remaining conductor pattern 67, 64 has astructure identical to that of the data wiring 62, 64, 65, 66, 68,except that the source electrode 65 and the drain electrode 66 are notseparated but connected with each other. In case dry etching is used,the photosensitive film pattern 112, 114 is also etched to some degree.

Next, the exposed intermediate layer 50 of the remaining part (B) andthe semiconductor layer 40 below it are removed by dry etching alongwith the first part 114 of the photosensitive film, as in FIGS. 17 a and17 b. Preferably, the etching is performed under a condition wherephotosensitive film pattern 112, 114, the intermediate layer 50 and thesemiconductor layer 40 are etched simultaneously (the semiconductorlayer and the intermediate layer have little etching selectivity) butthe gate insulation film 30 is not etched. Especially, it is preferredthat the photosensitive film pattern 112, 114 and the semiconductorlayer 40 are etched with almost the same etching ratios. For example, amixture gas of SF₆ and HCl or a mixture gas of SF₆ and O₂ may be used toetch the two films to almost the same thickness. In case the etchingratios of the photosensitive film pattern 112, 114 and the semiconductorlayer 40 are identical, thickness of the first part 114 should be equalto or smaller than the sum of thicknesses of the semiconductor layer 40and the intermediate layer 50.

As a result, the first part 114 of the channel part (C) is removed toexpose the conductor pattern for source/drain 67 and the intermediatelayer 50 and the semiconductor layer 40 of the remaining part (B) areremoved to expose the gate insulation film 30 below them, as in FIGS. 17a and 17 b. Also, the second part 112 of the data wiring part (A) isetched. In this process, a semiconductor pattern 42, 48 is completed.The drawing symbol 57 refers to an intermediate layer pattern below theconductor pattern for source/drain 67, and the drawing symbol 58 refersto an intermediate layer pattern below the conductor pattern formaintenance capacitor 64.

Photosensitive film remnants remaining on the surface of the conductorpattern for source/drain 67 of the channel part (C) are removed byashing.

Next, the conductor pattern for source/drain 67 of the channel part (C)and the intermediate layer pattern for source/drain 57 below it areremoved by etching, as in FIGS. 18 a and 18 b. Both the conductorpattern for source/drain 67 and the intermediate layer pattern 57 may bedry-etched; or it is possible to wet-etch the conductor pattern forsource/drain 67 and dry-etch the intermediate layer pattern 57. In theformer case, a condition where the etching selection ratio of theconductor pattern for source/drain 67 and the intermediate layer pattern57 is large is preferred. It is because if the etching selection ratiois not large, it is difficult to find the etching terminal point, sothat it is difficult to control the thickness of the semiconductorpattern 42 remaining in the channel part (C). In the latter case, astaircase shape is obtained because while the side of the conductorpattern for source/drain 67 is etched, the intermediate layer pattern 57is hardly etched. Examples of an etching gas used to etch theintermediate layer pattern 57 and the semiconductor pattern 42 are amixture gas of CF₄ and HCl and a mixture gas of CF₄ and O₂. If a mixturegas of CF₄ and O₂ is used, a semiconductor pattern 42 having a uniformthickness can be obtained. In this process, part of the semiconductorpattern 42 may be removed to reduce the thickness and the second part112 of the photosensitive film pattern is also etched to some degree, asseen in FIG. 15 b. The etching is performed under a condition where thegate insulation film 30 is not etched. A thick photosensitive filmpattern is preferable lest the second part 112 should be removed toexpose the data wiring 62, 64, 65, 66, 68 below it.

As a result, the source electrode 65 and the drain electrode 66 areseparated from each other and a data wiring 62, 64, 65, 66, 68 and acontact layer pattern 55, 56, 58 below it are completed.

Lastly, the second part of the photosensitive film 112 remaining in thedata wiring part (A) is removed. Removal of the second part 112 may alsobe performed after removing the conductor pattern for source/drain 67 ofthe channel part (C) and before removing the intermediate layer pattern57 below it.

As explained above, wet etching and dry etching can be used in turns oronly dry etching may be used. While the latter case is convenient inthat only one type of etching is used, it is difficult to find afavorable etching condition. On the other hand, while the former case isadvantageous in finding a favorable etching condition, the etchingprocess is more complicated than the latter case.

Next, a protection film 70 is formed by growing a silicon nitride film,an a-Si:C:O film or an a-Si:O:F film by the chemical vapor deposition(CVD) method, or by applying an organic insulation film, as in FIGS. 19a and 19 b.

Then, the protection film 70 is photo-etched along with the gateinsulation film 30 to form contact openings 76, 74, 78, 72 that exposethe drain electrode 66, the end part of the gate line 24, the end partof the data line 68 and the conductor pattern for maintenance capacitor64, respectively, as in FIGS. 20 a to 20 c. Preferably, areas of thecontact openings 74, 78 that expose the end parts 24, 68 range from 0.5mm×15 μm to 2 mm×6 μm.

Lastly, an ITO film or an IZO film is deposited to 400 Å to 500 Å ofthickness and photo-etched to form a pixel electrode 82 connected withthe drain electrode 66 and the conductor pattern for maintenancecapacitor 64 and a contact supporting member 88 connected with the endpart of the gate line 24, the contact supporting member 86 and the endpart of the data line 68, as in FIGS. 11 to 13.

Preferably, nitrogen gas is in the pre-heating process before depositingITO or IZO to prevent formation of metal oxidation film on the metalfilm 24, 64, 66, 68 exposed through the contact openings 72, 74, 76,78).

The second example of the present invention simplifies manufactureprocesses by forming the data wiring 62, 64, 65, 66, 68, the contactlayer pattern 55, 56, 58 below it and the semiconductor pattern 42, 48using one mask and separating the source electrode 65 from the drainelectrode 66, while offering the advantage of the first example of thepresent invention.

While the second example of the present invention also forms both thegate wiring and the data wiring in two layers, only one of the gatewiring or the data wiring may be formed in two layers, if necessary.

Since a thin film transistor substrate of the present inventioncomprises self-assembled monolayers between the substrate and the metalwiring, it has a good adhesion ability to the substrate and effectivelyprevents diffusion of the metal wiring material to the substrate.

1. A thin film transistor substrate comprising self-assembled monolayersbetween the substrate and a metal wiring.
 2. A thin film transistorsubstrate according to claim 1, wherein the self-assembled monolayersare formed by the compounds selected from a group consisting of3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane,2-aminoundecyltrimethoxysilane, aminophenyltrimethoxysilane,N-(2-aminoethylaminopropyl)trimethoxysilane, methyltrimethoxysilane,propyltriacetoxysilane, (3-mercaptopropyl)trimethoxysilane and(3-mercaptopropyl)trimethoxysilane.
 3. A thin film transistor substrateaccording to claim 1, wherein thickness of the self-assembled monolayersranges from 2 to 3 nm.
 4. A thin film transistor substrate according toclaim 1, wherein the metal wiring is made of copper or alloy of copperand metals selected from a group consisting of Ag, Mg, B, Ca, Al, Li,Np, Pu, Ce, Eu, Pr, La, Nd, Sm and Zn.
 5. A thin film transistorsubstrate according to claim 1, wherein the substrate is a glasssubstrate, an n+a-Si/a-Si/SiN three-layer substrate, or an Si, SiO₂ orother low-k (k<3.5) substrate.
 6. A thin film transistor substratecomprising: an insulation substrate; a first signal line formed on theinsulation substrate; a first insulation film formed on the first signalline; a second signal line formed on the first insulation film andcrossing the first signal line; a thin film transistor electricallyconnected with the first signal line and the second signal line; asecond insulation film formed on the thin film transistor and having afirst contact opening that expose an electrode of the thin filmtransistor; and a pixel electrode formed on the second insulation filmand connected to an electrode of the thin film transistor through thefirst contact opening, wherein at least one of the first signal line andthe second signal line has a copper or copper alloy wiring structureconsisting of a double layer of self-assembled monolayers and a Culayer.
 7. A thin film transistor substrate according to claim 6, whereinat least one of the first signal line and the second signal line has acopper or copper alloy wiring structure consisting of three layers ofself-assembled monolayers, an Ag layer and a Cu layer.
 8. A thin filmtransistor substrate comprising: a gate wiring formed on an insulationsubstrate and comprising a gate line and a gate electrode connected tothe gate line; a gate insulation film covering the gate wiring; asemiconductor pattern formed on the gate insulation film; a data wiringcomprising a source electrode and a drain electrode formed in the samelayer on the gate insulation film or on the semiconductor pattern, whichare separated from each other, and a data line connected to the sourceelectrode and crossing the gate line to define a pixel area; aprotection film having a first contact opening that exposes the drainelectrode; and a pixel electrode formed on the protection film andconnected with the drain electrode through the first contact opening,wherein at least one of the gate wiring and the data wiring has a copperor copper alloy wiring structure consisting of a double layer ofself-assembled monolayers and a Cu layer.
 9. A thin film transistorsubstrate comprising: an insulation substrate; a gate wiring formed onthe substrate and comprising a gate line, a gate electrode and an endpart of the gate line; a gate insulation film formed on the gate wiringand having a contact opening that exposes the end part of the gate line;a semiconductor pattern formed on the gate insulation film; a datawiring comprising a source electrode, a drain electrode, a data line andan end part of the data line that has a contact layer pattern on thegate insulation film or on the semiconductor pattern; a protection filmformed on the data wiring and having contact openings that expose theend part of the gate line, the end part of the data line and the drainelectrode; and a transparent electrode layer pattern electricallyconnected with the exposed end part of the gate line, end part of thedata line and drain electrode, wherein at least one of the gate wiringand the data wiring has a copper or copper alloy wiring structureconsisting of a double layer of self-assembled monolayers and a Culayer.
 10. A thin film transistor substrate according to claim 8 orclaim 9, which further comprise an ohmic contact layer formed betweenthe semiconductor pattern and the data wiring, wherein the ohmic contactlayer has a structure substantially identical to that of the datawiring.
 11. A thin film transistor substrate according to claim 8 orclaim 9, wherein the semiconductor pattern has a structure identical tothat of the data wiring except for the channel part.
 12. A metal wiringmethod of a thin film transistor substrate comprising: a step of coatinga coating composition for self-assembled monolayers (SAMs) formation ona substrate and heat-treating it; a step of depositing a metal wiringmaterial on the substrate; and a step of heat-treating the substrate.13. A copper wiring method of a thin film transistor substrate accordingto claim 12, wherein the substrate is a glass substrate, ann+a-Si/a-Si/SiN three-layer substrate, or an Si, SiO₂ or other low-k(k<3.5) substrate.